1. Field of the Invention
The present invention relates to a heat storage tank which stores a coolant of a liquid-cooled engine such as a water-cooled engine while being thermal-insulated.
2. Description of Related Art
For example, as disclosed in JP-A-2002-188442 (corresponding to U.S. Pat. No. 6,477,990), a heat storage tank is disposed in a cooling water circuit of a water-cooled engine, and stores high-temperature cooling water (coolant) therein in an engine operation. Then, the heat storage tank discharges the stored high-temperature cooling water to the engine at the next engine starting, thereby improving warming-up performance of the engine. Alternatively, heating performance of a heating unit can be improved using the cooling water (hot water) from the heat storage tank as a heat source.
The heat storage tank includes a tank body for storing high-temperature cooling water and a housing having a water passage communicating with the tank body. Further, the tank body and the housing are mechanically assembled to each other, so that cooling water in the water passage flows into and flows out of the tank body. Generally, an O-ring made of rubber is generally disposed between the tank body and the housing, so that a sealing performance can be obtained in the heat storage tank. However, in this case, the O-ring is exposed to both outside air and the high-temperature cooling water due to a vibration of a vehicle and a water pressure in the cooling water circuit. In this case, a rubber material readily deteriorates in high-temperature and oxidation conditions. Thus, the sealing performance of the cooling water in the heat storage tank may be deteriorated.